Respective methods and detectors are known in the prior art. A scintillator in a scintillation detector absorbs the radiation to be measured, thereby generating excited states within the scintillator. Those excited states decay with a decay time τ under the emission of light, whereas the amount of light is a measure for the absorbed energy of the incoming radiation. The light is directed to a photocathode, emitting electrons in dependence of the amount of light, being absorbed there, being usually amplified by photomultiplier. The output signal of the photomultiplier therefore is a measure for the total energy of the absorbed radiation.
It is known that the light output of a scintillator is dependent from its temperature, so that the output signal, being proportional to the measured energy, is also dependent from the temperature of the scintillator. As it is often not possible to operate the scintillation detector at a constant known temperature, the detector's accuracy of measurement is substantially impaired by the temperature changes.
According to the known prior art, this is achieved by a calibration, being applied before or after the measurement, whereas a so called calibration source, that is a radiation source with a known energy of radiation, is used for calibration. As an alternative or in addition, the calibration may be effected on the basis of known lines with known energy, being present in the measured spectrum.
This has the disadvantage that temperature changes, occurring between the time of calibration and the time of measurement, lead to an additional uncertainty of the measurement. Especially with detectors, being used under changing external operation conditions, especially outside of a laboratory, this disadvantage is of importance. Furthermore, it has often to be assumed, especially in security engineering—contrary to classical research applications—that they are not enough lines of previously known energy present within the spectrum, so that the measured spectrum has to be evaluated in advance in order to be able to allocate specific energies to single measured lines. Because of possible incorrect allocations, this is subject to errors. As the security personal usually has no nuclear physics knowledge, the allocation of single lines of the measured spectrum to specific known energies is a difficulty in addition.
Applicant therefore developed a scintillation detector and a method for operation of such a detector, in which the known energy of a calibration source can be measured continuously, or, as the case may be, in defined, comparably short time gaps, by the detector so that the detector could be calibrated during the measurement with the known energy of the radiation of the calibration source. Therewith it is possible also for persons without physics knowledge to collect a spectrum of ionizing radiation with high accuracy.
The radiation within the energy range of the radiation, being emitted from the calibration source, is nevertheless superposed by exactly this radiation of the radiation source and therefore not measured in an optimal manner. In case one does not calibrate the detector continuously, but, alternatively in larger time gaps, the radiation within the energy range of the calibration source could be measured also, nevertheless at the same time the energy resolution becomes worse by temperature changes not being picked up. Therefore, it is for principle reasons very difficult to achieve a high energy resolution by a continuous calibration with at the same time high sensitivity in the complete energy area, that is also in the area of the radiation, being emitted by the calibration source.
An additional problem is that, in order to calibrate for the measurement of an ionizing radiation, usually a radioactive calibration source is necessary, which usually is part of the detector if it is used for security engineering. This requires substantial efforts during the production of respective detectors. Because of continuously rising safety measures and the desire to avoid radioactive material as far as possible, there therefore is a need to calibrate scintillation detectors without the use of radioactive material.